Ignition system supplying continuous source of sparks

ABSTRACT

An ignition system providing a continuous source of spark ignition pulses for igniting a fuel-air mixture. The ignition system includes solid state circuit means for providing a substantially constant spark repetition rate and constant spark energy over a wide range of input voltages.

United States Pat ent Boyer May 30, 1972 [54] NITI N SYSTEM SUPPLYING3,223,887 12/1965 Brown ....315/2l9 X TIN 3,424,945 l/ 1969 Seider etal. 315/209 CD CON UOUS SOURCE OF SP 3,486,071 12/1969 Hedge ....33l/ ll 1 X [72] Inventor: Wesley D. Boyer, Franklin, Mich. 2,874,293 2/1959McMurren ..331/ 109 {73] Assignee; Ford Motor Company, Deal-born, Mich.mmary Examin Roy Lake 22 Filed: Apr. 3 19 9 Assistant Examiner-Palmer C.Demeo Attorney-John R. Faulkner and Keith L. Zerschling [21] App]. N0.Z813,002

[57] ABSTRACT [52] U.S. Cl ..315/219, 315/209 T, 331/1 1 1 An ignitionsystem providing a continuous source of spark i;- [51] Int. Cl. ..l'l05b37/02 nition pulses for igniting a fuel-air mixture. The ignition [58]Field of Search ..315/209 T, 209 CD, 219, 100 S; system includes solidstate circuit means for providing a sub- 331/111 stantially constantspark repetition rate and constant spark energy over a wide range ofinput voltages. [56] References Cited 8 C 9 6 Dnwing lures UNITED STATESPATENTS 2,480,681 8/1949 Stiefel ..315/100 S Patented May 30, 1972 2Sheets-Sheet 1 INVENTOR R 0 O 5 T WM wmw Patented May 30, 1972 3,666,989

2 Sheets-Sheet 2 INVENTOR Wilf/ Q .8074)? x; ATTORNE:S

IGNITION SYSTEM SUPPLYING CONTINUOUS SOURCE OF SPARKS BACKGROUND OF THEINVENTION This invention relates to an ignition system that provides acontinuous source of sparks for igniting a fuel-air mixture, and moreparticularly, to such a system that provides a constant spark repetitionrate and constant energy pulses over a wide range of input voltages.This system may be employed to ignite the fuel-air mixture in a burner,for example, a burner in a gas turbine engine.

There are many prior art ignition systems of the continuous spark typein which a train of ignition pulses is applied to a spark plug to ignitea fuel-air mixture. Such ignition systems may be employed to ignite thefuel-air mixture in the burner of the gas turbine engine.

The present invention provides an improvement over the prior artdevices. in that circuit means of the solid state type are connected toa source of electrical energy and this circuit means applies acontinuous train of substantially rectangular pulses to an energystorage device, for example, the primary winding of an ignition coil. Aspark igniter, or spark plug, is connected to the secondary winding ofthe ignition coil and will have high voltages produces across it whenthe current through the primary winding is periodically interrupted. Thesolid state circuit means includes means for generating substantiallyrectangular pulses that have substantially constant electrical energy ineach pulse and that have a substantially constant repetition rate overwide ranges of the terminal voltage of the source of electrical energyto which the circuit means is coupled. As a result, an ignition systemis provided that has low power consumption, reliable operation over wideranges of input voltages and regulated energy of the spark dischargeswhich are relatively unaffected by a continuous flame, i.e. ionizationof plasma in the spark gap.

The ignition system of the present invention overcomes the disadvantageor shortcoming of prior art systems, i.e., poor low input voltageperformance, by providing automatic and continuous compensation of thespark energy in direct response to input voltage fluctuations. Asmentioned above, this spark energy is maintained substantially constantover wide variations in the input voltage. Moreover, the solid statecomponents of the ignition system are protected against excessivecurrent surges that might occur at high input voltages or when a flamein the spark gap causes a high load component of current to be drawnthrough the ignition coil by transformer action.

SUMMARY OF THE INVENTION The ignition system of the present inventionincludes an electrical storage device, preferably in the form of aninductor which may by the primary winding of an ignition coil. Thesecondary winding of the ignition coil is connected to a spark gap inthe form of a spark plug. A solid state switching device, preferably inthe form of a transistor, is connected in series with a source of directcurrent electrical energy and the electrical storage device. Circuitmeans are connected to the source of electrical energy and the inputcircuit of the solid state switching device for switching it betweenconductive and nonconductive states. This means includes means formaintaining the energy in the output pulses from the solid stateswitching device substantially constant for wide variations in theterminal voltage of the source of electrical energy. Moreover, means areprovided in the circuit means for maintaining the repetition rate, i.e.,the time interval between successive switchings of the solid stateswitching device to its conductive state, substantially constant overwide variations in the input voltage, i.e. the terminal voltage of thesource of electrical energy.

This circuit means may take the form of an oscillator that producessubstantially rectangular voltage pulses, with the energy in the pulsesbeing substantially constant and with the repetition rate of the pulsesbeing substantially constant despite wide variations in the inputvoltage, i.e. the terminal voltage of the source of electrical energy.

The above purposes are accomplished by a first RC circuit connected tothe input of the solid state switching device through a transistorizedswitching network. This transistorized switching network will maintainthe solid state switching device in the conducting state until apredetermined charge or voltage appears across the capacitor. The solidstate switching device will be switched to its nonconducting state,thereby interrupting current through the primary winding of the ignitioncoil, when the voltage on the capacitor reaches this predeterminedlevel. The desired output energy level determines the choice of thispredetermined voltage level.

Additionally, a second RC circuit means is provided that charges throughthe base of a transistor. The capacitor of this second RC circuit isconnected across the solid state switching device and therefore isprevented from charging when the solid state switching device is in theconducting state. When the solid state switching device switches to thenonconducting state, however, this capacitor charges through thetransistor thereby switching it to a conducting state. Circuit means areconnected to the transistor for discharging the first capacitor when thetransistor is in the conducting state and circuit means are alsoconnected to the transistorized switching network and this transistorfor maintaining the solid state switching device in the nonconductingstate until such time as the second capacitor charges to a level wherethe current through the base of the transistor is no longer sufficientto maintain it in a conducting state. At this time the transistorswitches to a nonconducting state, the first capacitor again commencesto charge, the solid state switching device is switched to a conductingstate and the second capacitor discharges through the solid stateswitching device.

The time constants of the first and the second RC circuits are selectedso that the repetition rate of the rectangular pulses appearing at theoutput of solid state switching device and applied to the primarywinding of the ignition coil is substantially constant. Moreover, thefirst RC circuit insures that the energy in each voltage pulse, which isproportional to the voltsecond product squared, is substantiallyconstant irrespective of the terminal voltage of the source ofelectrical energy. When the terminal voltage of the source ishigh, thepulses will have a large magnitude but a relatively short time durationand the time that the transistor is maintained in a conductive statewill be large. On the other hand, when the terminal voltage of thesource of electrical energy is at a lower level, the magnitude of thepulse will be lower, but its width in terms of time will be larger andthe length of time that the transistor is in a conducting state will bereduced. Consequently, the time interval between the leading edges ofsuccessive rectangular pulses will be substantially constantirrespective of the terminal voltage of the source of electrical energy.

An object of the present invention is the provision ofa continuous sparkignition system that is reliable, that operates over a wide range ofinput voltages and that has low power consumption.

A further object of the invention is the provision of a continuous sparkignition system in which the repetition rate of the pulses of electricalenergy applied to a spark plug and the electrical energy in each pulseare substantially constant over wide variations of the terminal voltageof the source of electrical energy employed in the ignition system.

Other objects and attendant advantages of the present invention willbecome more readily apparent as the specification is considered inconnection with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of theignition system of the present invention.

FIG. 2 is a plot of the time that electrical energy is applied to theprimary winding of the ignition coil of the present invention whendifferent terminal voltages are available from a source of electricalenergy.

FIG. 3 is a plot showing the time that electrical energy is not appliedto the primary winding of the ignition coil when different terminalvoltages areavailable from a source of electrical energy.

FIG. 4 shows a rectangular voltage pulse train applied to the primarywinding of the ignition coil when the terminal voltage of the source ofelectrical energy is at a given magnitude.

FIG. 5 is a plot similar to FIG. 4, but showing pulses applied to theprimary winding of the ignition coil when the magnitude of the terminalvoltage of the source of electrical energy is somewhat lower, and 1 FIG.6 is a plot similar to FIGS. 4 and 5, but showing pulses applied to theprimary winding of the ignition coil when the magnitude of the terminalvoltage of the source of electrical energy is at still a lower level.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, thereis shown a source of direct current electrical energy 10 which may be inthe form of an electrical storage battery having a negative terminal 12connected to ground and a positive terminal 14 connected to a movableblade 16 of an ignition switch 18. A stationary contact 20 of theignition switch 18 is connected to a line 22 via junction 24.

The ignition system of the present invention includes an energy storagedevice in the form of an ignition coil 26 having an energy storageinductor or primary winding 28 and a secondary winding 30 connected to aspark discharge device or spark plug 32. i

The primary winding 28 of the ignition coil 26 is connected to thepositive terminal 14 of the source of electrical energy 10, whenignition switch 18 is closed, through a solid state switching device 34which may comprise a first transistor 36 and a second transistor 38. Oneoutput electrode, emitter 40, of the first transistor 36 is connected tothe junction 24, while the other output electrode, collector 42, isconnected to the primary winding 28 of the ignition coil 26 throughleads 44 and 46. Thecontrol electrode, base 48, of first transistor 36.is connected to an output electrode, emitter 50, of second transistor38, and the emitter 50, together with the control electrode, base 48,are connected through a resistor 52 to line 22. The other outputelectrode, collector 54, of second transistor 38 is connected to a lead56 having one end connected to ground through a resistor 58. The controlelectrode, base60, of second transistor 38 is connected to a junction 62between a resistor 64 and a resistor 66 that are connected in serieswith the output electrodes, i.e., collector 68 and emitter 70 of atransistor 72. The emitter 70 is in turn connected to a junction 74 thatis connected to one terminal of a resistor 76. The other terminal of theresistor 76 is connected to ground as shown in the drawing. The seriescircuit comprising resistor 64, resistor 66, the collector 68-emitter 70circuit of transistor 72 and resistor 76 is connected across the sourceof electrical energy 10, when ignition switch 18 is closed, by havingthe terminal of resistor 64 opposite junction 62 connected to line 22and by having the terminal of resistor 76 opposite junction 74 connectedto ground.

The base 78 of transistor 72 is connected through resistor 80 to line 22and is also connected to a collector 82 of transistor 84. The emitter 86of transistor 84 is connected to lead 88 through lead 90, and the lead88 is in turn connected to junction 74 and hence to ground throughresistor 76. The base 92 of transistor 84 is connected through lead 94to a junction 96. This junction 96 is in turn connected to grounded line98 through a resistor 100 and to collector 102 of transistor 104 througha series connected resistor 106 and diode 108.

The emitter 110 of transistor 104 is connected to the line 22, while thebase 112 is connected through resistor 114 to a junction 116. Thejunction 116 is connected to one terminal 1 18 of a capacitor 120, whilethe other terminal 122 of capacitor 120 is connected to line 56. A diode124 is connected between junction 116 and line 22, and hence across thebase 112-emitter 1 l0 circuit of transistor 104.

A resistor 126 has one terminal connected to line 22 via lead 128 andthe other terminal connected to a junction 130 via lead 132. .Thejunction 130 is in turn connected to one terminal 134 of a capacitor136, and the other terminal 138 of capacitor 136 is connected to line 88and hence to ground through resistor 76. A zener diode 140 has itscathode 142 connected to junction 130 and its anode 144 connected to theanode 146 of diode 148. The cathode 150 of diode 148 is in turnconnected to junction 96.

Another transistor 156 has its emitter 158 connected tothe line 98 andhence to ground, its collector 160 connected to junction 130 and itsbase 162 connected to collector 102 of transistor 104 via lead 164,resistor 166 and lead 168. Thus, the output circuit of transistor 156 isconnected across the series circuit comprised of capacitor 138 andresistor 76.

In addition, the ignition system of the present invention includes atransient suppression capacitor 170 connected across lines 22 and 98,and a zener diode 172 connected acros the emitter and collector 42 oftransistor 36. This zener diode serves to protect the transistor 36against high reverse voltages that occur when current through primarywinding 28 of ignition coil 26 is interrupted. I

OPERATION It is considered best for the purposes of understanding theoperation of the present invention to assume that the circuit isinitially deenergized so that both capacitors 120 and 136 are uncharged.When ignition switch 18 is closed, the terminal voltage of the source ofelectrical energy 10 will be applied to line 22. Current will flow fromthis linethrough resistor 80 through base 78 and emitter 70 oftransistor 72 and then to ground through resistor 76, thereby switchingtransistor. 72 to a fully conducting state. This will permit currentflow out of base 60 of transistor 38 through resistor 66 and thecollector 68-emitter 70 circuit of transistor 72 to ground through-resistor 76 thereby switching transistor 38 to its fully conductingstate. This permits current flow out of base 48 of transistor 36 therebyswitching it to its fully conducting state. The switching of transistor36 to its fully conducting state immediately applies the terminalvoltage of the source of electrical energy 10 to the primary winding 28of ignition coil 26 and current begins to flow and build up in primarywinding 28.

When the solid state switching device 34 comprised of transistors 36 and38 is in its conducting state as described above, the two terminals 1 l8and 122 of capacitor are essentially shortcircuited through the solidstate switching device thereby preventing the charging of capacitor 120,and preventing current flow into the base 112 of transistor 104.Transistor 104 is thereby held in a nonconducting state. Simultaneouswith the flow of current through resistor 80to switch transistor 72 andhence transistors 38 and 36 of solid state switching device 34 to theirconducting states, current will flow through lead 128 and resistor 126into capacitor 136, thereby charging this capacitor. During the initialstages of the charging of capacitor 136, the zener diode 140 preventscurrent flow from junction toward junction 96 and thereby preventingcurrent flow into base 92 of transistor 84. As a result, transistor 84is held in a nonconducting state. Since transistor 104 is also in anonconducting state at this time, transistor 156 is held in anonconducting state since no current can flow into its base 162 fromcollector 102 of transistor 104.

The values of resistor 126 and capacitor 138 are chosen so thatcapacitor 138 charges to a threshold voltage equal to the zenerbreakdown voltage of zener diode plus the forward voltage drop acrossdiode 148 and the forward voltage drop across the base 92-emitter 86circuit of transistor 84 in a time period which is a function of theterminal voltage at source 10. When this voltage is reached, the zenerdiode 140 breaks down and current flows through zener diode 140 fromjunction 130 through diode 148 and through the base 92-emitter 86circuit of transistor 84 to ground. This prevents further build-up ofvoltage on capacitor 136 and switches transistor In the transmissionsystem according to the invention the transmission of the address signaltakes place in this manner without frequency separation and without timeseparation within the speech band, while nevertheless the speech qualityis substantially not influenced by the address signal.

FIG. 3 shows a variation of the transmission system accordin g to theinvention in which elements corresponding to FIG. 1 are denoted by thesame reference numerals.

The difference of this transmission system with respect to that shown inFIG. 1 lies in the construction of the modulation device 19 which inthis system consists of a modulo-2-adder 25 preceded by a limiter 26 sothat the received information signals are converted into a bivalentsignal.

The operation of the receiver corresponds essentially to that of thereceiver shown in FIG. 1; in particular, the integration voltageoccurring at the output of the integrating network 20 also shows thevariation as shown in FIG. 20.

However, the construction of the receiver shown in FIG. 3 is to bepreferred since the modulo-Z-adder 25 preceded by a limiter 26constitutes a simpler and more reliable modulation device than theproduct modulator used in FIG. 1.

FIG. 4 shows a preferred embodiment of the transmission system accordingto the invention in which elements corresponding to FIGS. 1 and 3 areagain denoted by the same reference numerals. Instead of a singlemodulation device as in FIGS. 1 and 3, a double modulation device isused.

In the embodiment shown the modulation device 19 comprises twomodulo-2-adders 27, 28 which are connected with their first inputs inparallel arrangement to the limiter 26 and the output terminals of whichare connected to a linear difference producer 29 the output voltage ofwhich is applied to the integrating network 20. The local pulse patterna(t 'r+D) advanced over one shift period D is applied to the secondinput of the modulo-Z-adder 27, while the second input of themodulo-Z-adder 28 is applied the local pulse pattern a(t -r D) delayerover one shift period D, which advanced and delayed local pulse patternsare derived from the outputs of the shift register elements 14' and 11respectively. An integration voltage will then be formed at the outputof the integrating network 20 which voltage as a function of the timedelay r has the variation as shown in FIG. 2f with a radial symmetry for-r 0. The control of the switch 7 preceding the reproduction device 6 iseffected in this case by the output voltage of the modulo-2-adder 28through a smoothing filter 30 in the form of an integrating network.

In the same manner as explained with reference to the transmissionsystems shown in FIGS. 1 and 3 a phase stabilization is obtained in thiscase of the local clock pulse generator 16' at the phase of the pulsepattern generated at the transmitter end. The double construction of themodulation device 19, however, presents the advantage that the variationof the integration voltage shown in FIG. 2f makes it possible that thetime delay 'r of the local pulse pattern a(t 7') with respect to theoriginal pulse pattern a(t) which is already small in the case of phasestabilization can now be reduced to substantially zero.

The above described transmission systems according to the invention arealways constructed for the transmission of one speech signal as a maininformation signal, while an address signal is always used as anauxiliary information signal.

In the embodiments shown in FIGS. 5 and 6 on the contrary a large numberof main information signals are transmitted through a commontransmission path successively in time multiplex, the auxiliaryinformation signal being used as a synchronization signal in restoringthe individual main information signals at the receiver end.

The transmission system according to the invention shown in FIG. 5 isconstructed for the transmission of a number of speech signals, eachoriginating from an individual signal source 31, 32 33 and each having abandwidth of, for example, 0-4 KI-Iz. At the transmitter end in thistransmission system each source 31, 32. 33 is connected, through anindividual line including analog-to-digital converters 34, 35.

36, for example, in the form of a deltamodulator, to one of the inputs37, 38. 39 of commutator 40 by means of which the speech signals in adigital form are transmitted successively in time multiplex through atransmission path 41. At the receiver end each of the speech signals isrestored in a digital form from the transmitted time multiplexing signalby means of a corresponding commutator 42 and applied to one of thecommutator outputs 43, 44. 45 which are each connected, throughindividual lines in which digital-to-analog converters 46, 47 ,48corresponding to the analog-to-digital converter are incorporated, forexample, in the form of an integrating network associated with thedelta-modulator, to a separate load 49, 50 51. i

For controlling the commutator 40 at the transmitter end the clock pulsegenerator 16in the pulse pattern generator 8 which is constructed in thesame manner as in the preceding transmission systems, is also connectedto a control circuit 52 of the commutator 40, the control I circuit 52detennining which commutator input 37, 38. 39 is connected to thetransmission path 41 at a given instant. The initial position of thecorrunutator 40 in which, for example, the first commutator input 37 isconnected to the transmission path 41, is coupled with a given conditionof the shift register 10in the pulse pattern generator 8, whichcondition, as is known, occurs only once per period T of the generatedperiodic pulse pattern. For that purpose, in the embodiment shown,theoutput of each shift register element ll, 12, 13, 14, l5.is connected toan individual input of an AND-gate 53 which supplies an output pulseonly when simultaneously a pulse appears at the output of all the shiftregister elements 11, 12, 13,14 and 15, which output pulse each timeresets the commutator 40 to its initial position through the controlcircuit 52.

At the receiver end the control of the commutator 42 is effected inquite the same manner as at the transmitter end, corresponding elementsin FIG. 5 for the devices being denoted by the same reference numeralsbut being provided with an index.

For the mutual synchronization of the commutators 40, 42 at thetransmitter and receiver ends a synchronization signal is alsotransmitted in this transmission system together with the speech signalsfor which, as already described above, no additional frequency and timespace is necessary.

For that purpose, at the transmitter end the pulse pattern occurring atthe output of the pulse pattern generator 8 is added as asynchronization signal by means of linear combination devices 54, 55. 56without frequency separation and without time separation to each speechsignal within the speech band of 0-4 Kl-Iz. At the receiver end therestored infonnation signals, consisting of the speech signals and thesynchronization signals added to each of them, are combined in a linearcombination device 57 and, like the locally generated pulse pattern,applied to the modulation device 19 which is constructed in the manneralready described with reference to FIG. 3 and the output voltage ofwhich controls the frequency corrector 21 connected to the local clockpulse generator 16' through the integrating network 20.

In the manner already described above in detail a phase stabilization onthe local clock pulse generator 16 at the phase of the pulse patternproduced at the transmitter end is obtained, said pulse pattern and thelocal pulse pattern coinciding and consequently also the conditions ofthe shift registers 10, 10' at the transmitter and receiver ends beingthe same at any moment so that an accurate synchronization of thecommutators 40, 42 at the transmitter and receiver ends is obtained.

Influencing of the speech quality by the synchronization signal can bereduced particularly efficiently in this case by using the measuresalready described above and not shown in the FIG. 5, for example,subtracting the local pulse pattern from the restored informationsignals and including deemphasis networks, while in the transmissionsystem shown in FIG. 5 a further reduction is possible since in thecombination of the restored information signals at the receiver end theDiode l48-lN-400l Diode 108-IN-400l Diode l24-lN-400l Diode l72-C5TF- l2A039-A Resistor 166-100K ohms Resistor l26-l 8K ohms Resistor 106- 1 Kohms Resistor l l4-100K ohms Resistor 80- l ,500 ohms Resistor l0047Kohms Resistor 76-10 ohms Resistor 66-100 ohms 2 watt Resistor 64-100ohms Resistor 52-27 ohms Resistor 58-7.5 ohms Capacitor 170-40 MMfd, 50volts Capacitor 1360.22 MMfd. X 10% -35 volts-tantalum Capacitor l-0.02MMfd.-200 volt-disc All Resistors '6 watt unless otherwise specified.

Thus, the present invention provides a reliable ignition system thatproduces a continuous series of spark ignition pulses having asubstantially constant repetition rate and having substantially constantenergy over wide ranges in the terminal voltage of the source ofelectrical energy employed to energize the ignition system.

The invention disclosed will have many modifications which will beapparent to those skilled in the art in view of the teachings of thisspecification. It is intended that all modifica tions which fall withinthe true spirit and scope of this invention be included with the scopeof the appended claims.

I claim:

1. In an ignition system for supplying a continuous source of sparkignition pulses having substantially constant energy and a substantiallyconstant repetition rate comprising an ignition coil having a primarywinding and a secondary winding, a spark plug connected to saidsecondary winding, a source of direct current electrical energy, a solidstate switching device having anoutput circuit and an input circuit,said output circuit connected in series with said primary winding ofsaid ignition coil, means coupled to said source of electrical energyand to the input circuit of said solid state switching device forperiodically switching said solid state switching device between itsconducting and nonconducting states, said means including a first RCcircuit comprising a series connected resistor and capacitor connectedacross said-source of electrical energy and a second RC networkcomprising a series connected resistor and capacitor connected acrosssaid source of electrical energy, means coupling said first RC circuitand said input circuit of said solid state switching device forswitching said solid state switching device to a nonconducting statewhen current through the primary winding and the voltage on thecapacitor of said first RC circuit reaches a predetermined value, andmeans coupled to said second RC circuit, said input circuit of saidsolid state switching device and said first RC circuit for permittingcurrent flow into said second RC circuit when said solid state switchingdevice is switched to its nonconducting state, and means coupled to saidsecond RC circuit and the input circuit of said solid state switchingdevice for switching said solid state switching device to a conductingstate when the voltage across the capacitor of said second RC circuitreaches a predetermined fraction of the terminal voltage of said sourceof electrical energy.

2. An ignition system comprising a spark plug, an ignition coil having aprimary and a secondary winding, a source of electrical energy, theterminal voltage of which may vary over wide limits, an electroniccircuit means coupled to said source of electrical energy and saidprimary winding, said electronic circuit means including a solid stateswitching device having an output circuit and an input circuit, saidoutput circuit of said solid state switching device connected in serieswith said source of electrical energy and said primary winding, acapacito a nonconducting state thereby interrupting current flow inprimary winding when said capacitive means is charged to a predeterminedvoltage level corresponding to a predetermined current level in saidprimary winding, said predeter mined voltage level being lower-than thelowest terminal voltage of said source of electrical energy whereby thevoltage delivered to said spark plug is substantially constantirrespective of wide variations of the terminal voltage of said sourceof electrical energy, and a second capacitive means, a transistor havinga base, an emitter electrode and a collector electrode, one of saidelectrodes being coupled to said source of electrical energy, meansconnecting said second capacitor meansto the base of said transistor,and across the output circuit of said solid state switching meanswhereby said second capacitive meansis prevented from being charged whensaid solid state switching device is in a conducting state and saidtransistor is maintained in a nonconducting state, said transistor beingswitched to a conducting state by current flow through said base andinto said second capacitive means when said solid state switching meansis switched to a nonconduetive state, first circuit means coupled to oneof said electrodes of said transistor and said first capacitive meansfor discharging said first capacitive means when said transistor is in aconducting state, second circuit means coupled to one of said electrodesof said transistor and the input circuit of said solid state switchingmeans, said transistor ceasing conduction when the voltage across saidsecond capacitive means is charged to a voltage level where insufficientcurrent flows through said base of said transistor to maintainconduction whereby said solid state switching means is switched to aconducting state and said first capacitive means commences to change.

3. The combination of claim 2 in which the time constants of said firstcapacitive means and said second capacitive means are selected tomaintain the time period between successive switchings of said solidstate switching means a conductive state essentially constant over widevariations in the terminal voltage of said source of electrical energy.

4. The combination of claim 3 in which said first circuit means includesa solid state switching means, said solid state switching means havingan output circuit connected across said first capacitive means and acontrol electrode connected to one of the electrodes of said transistor.

5. The combination of claim 4 in which said second'circuit meanscomprises a solid state switching network having an input circuitconnected to .said one of said electrodes of said transistor and anoutput circuit connected to the input circuit of said solid stateswitching device.

6. An ignition system comprising a spark plug, a source of directcurrent electrical energy, an inductor connected in series with saidsource of direct current electrical energy and adapted to be charged toa predetermined current level for providing a predetermined energycharge to the spark plug, a capacitor connected to said source ofelectrical energy, means coupled to said capacitor for limiting thevoltage across said capacitor to a predetermined voltage level lowerthan the voltage of said source of direct current electrical energy,means coupled to said capacitor and said source of electrical energy forcausing said capacitor to charge to said predetermined voltage level atthe same time the current through said inductor reaches thepredetennined level, and means coupled to said inductor, said capacitorand said means coupled to said capacitor for limiting the voltage acrosssaid capacitor, for interrupting current through said inductor when thepredetermined voltage across said capacitor is reached, and meanscoupled to said source of electrical energy, said capacitor, and saidlast mentioned means for discharging said capacitor and for restoringcurrent through said inductor at a time interval after the currentthrough the inductor has been interrupted,

said last mentioned means including means for causing said time intervalto vary as a function of the terminal voltage of said source ofelectrical energy.

7. In an ignition system, a spark plug, an ignition coil having aprimary and a secondary winding, a source of direct current electricalenergy, means coupling said secondary winding of said ignition coil tosaid sparkplug, and circuit means coupled to said source of directcurrent electrical energy and to said primary winding of said ignitioncoil for applying a series of voltage pulses having a substantiallyconstant repetition rate and substantially constant electrical energy tosaid primary winding over wide ranges of the terminal voltage of saidsource of electrical energy, said circuit means including a solid stateswitching device having an output circuit and an input circuit, saidoutput circuit connected in series with said source of electrical energyand said primary winding of said ignition coil, a voltage responsivemeans coupled to the input circuit of said solid state switching devicefor switching said solid state switching device to a nonconducting statewhen the voltage on said voltage responsive means is at a predeterminedvalue, and current responsive means coupled to the input circuit of saidsolid state switching device for switching said solid state switchingdevice to a conducting state when the current through said currentresponsive device is at a predetermagnitude.

8. In an ignition system, a sparkplug, an ignition coil having a primaryand a secondary winding, a source of direct current electrical energy,means coupling said secondary winding of said ignition coil to saidspark plug, and an oscillator coupled to said source of direct currentelectrical energy and to said 1 primary winding of said ignition coilfor applying a series of substantially rectangular voltage pulses havinga substantially constant repetition rate and substantially constantelectrical energy to said primary winding over wide ranges of theterminal voltage of said source of electrical energy, said oscillatorcomprising a solid state switching device having first and second outputelectrodes and a control electrode, said first and second outputelectrodes being connected in series with said source of electricalenergy and said primary winding of said ignition coil, a firstcapacitor, means coupling said source of electrical energy and saidfirst capacitor for charging said first capacitor from said source ofelectrical energy, circuit means coupled to said source of electricalenergy, to one terminal of said first capacitor and to said controlelectrode of said solid state switching device for maintaining saidsolid state switching device in a conducting state as said firstcapacitor charges to a predetermined voltage level and for switchingsaid solid state switching device to a nonconducting state when saidfirst capacitor charges to said predetermined voltage level, a secondcapacitor having a first terminal and a second terminal connected acrosssaid first and second output electrodes of said solid state switchingdevice, and current responsive means coupled to said source ofelectrical energy and said second capacitor for charging said secondcapacitor therethrough, said current responsive means switching saidsolid state switching device to a conducting state when currenttherethrough declines to a predetermined level as said second capacitorcharges to a predetermined voltage level.

* 1F I! l:

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,666,989 Dated May 30, 1972 Inventor(s) Wesley D. Boyer It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Cancel columns 5 and 6 and insert the following pages:

its conducting state Switching of transistor 8 to its conducting statediverts current from base 78 of transistor 72 and switches it to anonconducting state This blocks current flow out of the base 60 oftransistor 38,

' switching it to its nonconducting state, thereby blocking current flowout of base 48 of transistor 36 and switching it to its nonconductingstate. Switching of transistor 36 to a nonconducting state abruptlyinterrupts current through primary winding 28 of ignition coil 26 .andcauses a high voltage to be generated in secondary winding 30 andapplied to spark discharge device or plug 32.

of transistors 38 and 36, is switched to its nonconducting 'ORM (1059)USCOMM-DC 60376-P69 a UVSI GOVERNMENT PRINTING OFFICE I 1959 0-356-33.

3, ,9 9 May 30,. 1972 Wesley D. Boyer PAGE 2 state, the capacitor 120 isno longer shortcircuited.

Since terminal 122 of capacitor 120 is connected to ground via lead 56and resistor 58 current flows from line 22 through the emitter llQ base112 circuit of transistor 10 1 and.resistor 11 4 to terminal 118 ofcapacitor 120,

thereby initiating charging of capacitor 120. Current flow through theemitter 11o base 112 circuit of transis tor 10 1, switches it to itsconducting state. Current will therefore flow out of collector 102 andinto the base 92 of transistor 84 via resistor 106, diode 108, junction96 and lead 9 thereby latching transistor 84 in its conducting state andlatching transistors 72, 38 and 36 in their nonconducting states whentransistor 10 1 is in a conducting state, current will flow fromcollector 1 02 of transistor 10 1" into base 162 of transistor 156 vialead 168, resistor 166 and lead 16 1 thereby switching transistor 156 toits conducting state. This provides a discharge path for capacitor 136,and it will discharge through junction 130, collector 160 and emitter158 of transistor 156, line 98, resistor 76 and lead 88. Resistor 76 hasa very small I value, for example, 10 ohms, so that capacitor 52% may bedischarged in a very short time period.

The resistor 11 1 and capacitor 120 serve as a differentiating networkfor the voltage applied to line 22,

i.e. the terminal voltage of the source of electrical energy 10, and thecurrent through the emitter llO base 112 circuit of transistor 10 1 willdecay exponentially as the voltage on capacitor 12Q builds up. when thiscurrent drops to a given threshold current, below the base current,

3, 6, 989 May 30, 1972 Wesley D. Boyer PAGE 3 I necessary to sustainconduction of transistor 10, transistor 10 will switch to itsnonconducting state It can be appreciated that when transistor lO lswitches to its nonconducting state, transistor 156 is switched to itsnonconducting state, as well as transistor 8 L. Switching of transistor156 to a nonconducting state permits voltage to build up again acrosscapacitor 136, while switching of transistor 8 to its nonconductingstate switches transistor 72 to its conducting state As explainedpreviously,

when transistor 72 switches to its conducting state, the solid stateswitching device 3 L comprised of transistors 38 and 36 also switches toits conducting state and the full terminal voltage of the source ofelectrical energy 10 is again applied to the primary winding 28 of theignition coil 26. The cycle described above then repeats continuously.

It can be readily appreciated from the above description that asubstantially rectangular train of voltage pulses is applied to theprimary winding 28 of the ignition coil 26. This train of voltagepulses, that appear on lines M and L6, is shown in Figure l for aterminal voltage of the source of electrical energy 10 equal to somearbitrary constant value, V Referring now to Figure 2, there is shownthe voltage that would appear across capacitor 136 as a function of timefor three dif-.

ferent values, V3, V and V of the terminal voltage of the source ofelectrical energy 10. The voltage Vf is equal to the zener breakdownvoltage of zener diode l LO plus the forward voltage drop of diode 1&8plus the forward drop through the base 92 emitter 86 circuit of3,666,989 wa 20, .1972 Wesley D. Boyer PAGE 4 transistor 8 This voltagevalue is shown in the dotted line and is substantially below theterminal voltages, V3, V or V of the source of electrical energy 10. Itis preferred that the value of this voltage, V shown at the dotted linebe such that the voltage build-up across I capacitor prior to reachingthis threshold voltage be linear as shown for the values of terminalvoltage V V and V It will be seen that this voltage is reached in time Tfor terminal voltage V T for terminal voltage 3 3 V and T. for terminalvoltage V Referring now to Figure 3, there is shown a plot of currentsthrough the emitter l-lO base 112 circuit of transistor 10A for thedifferent values, V V and V of the terminal voltage of source 10. Thedotted line shows the current l at which the transistor 10 r will switchinto its nonconducting state This current is reached in time T for aterminal voltage equal to V Hence, the pulse appearing at the output ofthe solid state switching device 34 and that is applied to the primarywinding 28 will have a width equal to time T with a time spacing betweenthe trailing edge of the pulse and the leading edge of the next pulseequal to T with respect to the current shown in Figure 3, it can beappreciated that it is a decaying exponential brought about by thecharging of capacitor 120 and has an initial value equal to the terminalvoltage of the source of electrical energy 10 divided by the value ofresistor 114. v

If the terminal voltage of the source 10 is at a lower value, i.e V themagni tude of the pulse appearing at the output of the solid stateswitching device 3 1 3, ,989 May 30, 1972 Wesley -D. Boyer PAGE 5 willbe reduced to the value of V as shown in Figure 5. Its time width,however, will be equal to T as shown in Figure 2 and the time betweenthe trailing edge of the pulse and the leading edge of the next pulsewill be equal to '1'5 so that the pulse train will have a configurationas shown in Figure 5. On the other hand, if the terminal voltage ofsource 10 is at still a lesser value, V the magnitude of the pulse willbe that shown in Figure and is equal to V Its width in terms of time isequal to T as shown in Figure 2, while the time between the trailingedge of the pulse and the leading edge of the next successive pulse isequal to T as shown in Figure 3. The time width, T3, T and T of thepulses shown in Figures 4, 5 and 6, respectively, is a function of thetime constant of the RC network comprised of resistor 126 and capacitor136 and the terminal voltage of source 10. Similarly, the

times T T and T the time that the solid state switching device 3 is inthe nonconducting state, for a different value of the terminal voltageof source 10 is a function of the time constant of the RC circuitcomprised of resistor 11 4 and capacitor 120 and the terminal voltage ofthe source 10. By proper selection of the time constants of the RCnetwork comprised of resistor 126 and capacitor 136 and of the RCnetwork comprised of resistor 11M and capacitor $22, the pulserepetition rate will be substantially constant over a wide range ofterminal voltages of the source of electrical energy 10 as illustratedin the Figures 4, 5 and 6. The pulse repetition rate is equal to T plusT T plus T5, and T plus T as shown in Figures 2 and 3 for the differentvalues of terminal 3,666,989 M y s 19?2 Wesley De Boyer PAGE 6 voltage VV and V Similarly, it can be appreciated that the volt seconds appliedby each of the pulses shown in the Figures l, 5 and 6 is substantiallyconstant, since the time 'width increases proportionally to' thedecrease in the magnitude of the terminal voltage of the source 10.

This is brought about because of the operation of the I capacitor 136 isthe switching of the solid state switching device 3 and the linear rangeof its charging curve shown at Figure 2. l

A typical parts list for a pulse repetition rate of lOrO pulses persecond and a nominally ten ampere peak primary current in primarywinding 28 is given below; It

is readily apparent, of course, that for different peak primary currentsand different pulse repetition rates "the values of the resistors 126and 11A and the values of capacitors 136 and 120 may be changed orsuitably adjusted.

1 Typical Parts List Transistor 38 MJE 371 Transistor 36 C5TF l2AO27-A IM f 3" I Diode 1 40 MZ '5oo 3 UNITED STATES PATENT OFFICE QETEFICATE GECG T EC'HQN Patent No. 3,666, 989 Dated lnventofls) Wesley D. Boyer PAGE7 It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Signed and sealed this 26th day of December 1972.

(SEAL) Attest:

EDWARD WFLETCHERJR. ROBERT GOTTSCHALK Attesting Officer Commissioner ofPatents USCOMM-DC 60376-P69 FORM PO-10S0 (10-69) 1 us. GOVERNMENTPRINTING OFFICE: I969 o-ase-saa.

1. In an ignition system for supplying a continuous source of sparkignition puLses having substantially constant energy and a substantiallyconstant repetition rate comprising an ignition coil having a primarywinding and a secondary winding, a spark plug connected to saidsecondary winding, a source of direct current electrical energy, a solidstate switching device having an output circuit and an input circuit,said output circuit connected in series with said primary winding ofsaid ignition coil, means coupled to said source of electrical energyand to the input circuit of said solid state switching device forperiodically switching said solid state switching device between itsconducting and nonconducting states, said means including a first RCcircuit comprising a series connected resistor and capacitor connectedacross said source of electrical energy and a second RC networkcomprising a series connected resistor and capacitor connected acrosssaid source of electrical energy, means coupling said first RC circuitand said input circuit of said solid state switching device forswitching said solid state switching device to a nonconducting statewhen current through the primary winding and the voltage on thecapacitor of said first RC circuit reaches a predetermined value, andmeans coupled to said second RC circuit, said input circuit of saidsolid state switching device and said first RC circuit for permittingcurrent flow into said second RC circuit when said solid state switchingdevice is switched to its nonconducting state, and means coupled to saidsecond RC circuit and the input circuit of said solid state switchingdevice for switching said solid state switching device to a conductingstate when the voltage across the capacitor of said second RC circuitreaches a predetermined fraction of the terminal voltage of said sourceof electrical energy.
 2. An ignition system comprising a spark plug, anignition coil having a primary and a secondary winding, a source ofelectrical energy, the terminal voltage of which may vary over widelimits, an electronic circuit means coupled to said source of electricalenergy and said primary winding, said electronic circuit means includinga solid state switching device having an output circuit and an inputcircuit, said output circuit of said solid state switching deviceconnected in series with said source of electrical energy and saidprimary winding, a capacitive means, means coupled to said source ofelectrical energy and said capacitive means for charging said capacitivemeans at a predetermined time rate, and means coupled to said capacitivemeans and said input circuit of said solid state switching device forswitching said solid state switching device to a nonconducting statethereby interrupting current flow in primary winding when saidcapacitive means is charged to a predetermined voltage levelcorresponding to a predetermined current level in said primary winding,said predetermined voltage level being lower than the lowest terminalvoltage of said source of electrical energy whereby the voltagedelivered to said spark plug is substantially constant irrespective ofwide variations of the terminal voltage of said source of electricalenergy, and a second capacitive means, a transistor having a base, anemitter electrode and a collector electrode, one of said electrodesbeing coupled to said source of electrical energy, means connecting saidsecond capacitor means to the base of said transistor, and across theoutput circuit of said solid state switching means whereby said secondcapacitive means is prevented from being charged when said solid stateswitching device is in a conducting state and said transistor ismaintained in a nonconducting state, said transistor being switched to aconducting state by current flow through said base and into said secondcapacitive means when said solid state switching means is switched to anonconductive state, first circuit means coupled to one of saidelectrodes of said transistor and said first capacitive means fordischarging said firsT capacitive means when said transistor is in aconducting state, second circuit means coupled to one of said electrodesof said transistor and the input circuit of said solid state switchingmeans, said transistor ceasing conduction when the voltage across saidsecond capacitive means is charged to a voltage level where insufficientcurrent flows through said base of said transistor to maintainconduction whereby said solid state switching means is switched to aconducting state and said first capacitive means commences to change. 3.The combination of claim 2 in which the time constants of said firstcapacitive means and said second capacitive means are selected tomaintain the time period between successive switchings of said solidstate switching means a conductive state essentially constant over widevariations in the terminal voltage of said source of electrical energy.4. The combination of claim 3 in which said first circuit means includesa solid state switching means, said solid state switching means havingan output circuit connected across said first capacitive means and acontrol electrode connected to one of the electrodes of said transistor.5. The combination of claim 4 in which said second circuit meanscomprises a solid state switching network having an input circuitconnected to said one of said electrodes of said transistor and anoutput circuit connected to the input circuit of said solid stateswitching device.
 6. An ignition system comprising a spark plug, asource of direct current electrical energy, an inductor connected inseries with said source of direct current electrical energy and adaptedto be charged to a predetermined current level for providing apredetermined energy charge to the spark plug, a capacitor connected tosaid source of electrical energy, means coupled to said capacitor forlimiting the voltage across said capacitor to a predetermined voltagelevel lower than the voltage of said source of direct current electricalenergy, means coupled to said capacitor and said source of electricalenergy for causing said capacitor to charge to said predeterminedvoltage level at the same time the current through said inductor reachesthe predetermined level, and means coupled to said inductor, saidcapacitor and said means coupled to said capacitor for limiting thevoltage across said capacitor, for interrupting current through saidinductor when the predetermined voltage across said capacitor isreached, and means coupled to said source of electrical energy, saidcapacitor, and said last mentioned means for discharging said capacitorand for restoring current through said inductor at a time interval afterthe current through the inductor has been interrupted, said lastmentioned means including means for causing said time interval to varyas a function of the terminal voltage of said source of electricalenergy.
 7. In an ignition system, a spark plug, an ignition coil havinga primary and a secondary winding, a source of direct current electricalenergy, means coupling said secondary winding of said ignition coil tosaid sparkplug, and circuit means coupled to said source of directcurrent electrical energy and to said primary winding of said ignitioncoil for applying a series of voltage pulses having a substantiallyconstant repetition rate and substantially constant electrical energy tosaid primary winding over wide ranges of the terminal voltage of saidsource of electrical energy, said circuit means including a solid stateswitching device having an output circuit and an input circuit, saidoutput circuit connected in series with said source of electrical energyand said primary winding of said ignition coil, a voltage responsivemeans coupled to the input circuit of said solid state switching devicefor switching said solid state switching device to a nonconducting statewhen the voltage on said voltage responsive means is at a predeterminedvalue, and current responsive means coupled to the input circuit of saidSolid state switching device for switching said solid state switchingdevice to a conducting state when the current through said currentresponsive device is at a predetermagnitude.
 8. In an ignition system, asparkplug, an ignition coil having a primary and a secondary winding, asource of direct current electrical energy, means coupling saidsecondary winding of said ignition coil to said spark plug, and anoscillator coupled to said source of direct current electrical energyand to said primary winding of said ignition coil for applying a seriesof substantially rectangular voltage pulses having a substantiallyconstant repetition rate and substantially constant electrical energy tosaid primary winding over wide ranges of the terminal voltage of saidsource of electrical energy, said oscillator comprising a solid stateswitching device having first and second output electrodes and a controlelectrode, said first and second output electrodes being connected inseries with said source of electrical energy and said primary winding ofsaid ignition coil, a first capacitor, means coupling said source ofelectrical energy and said first capacitor for charging said firstcapacitor from said source of electrical energy, circuit means coupledto said source of electrical energy, to one terminal of said firstcapacitor and to said control electrode of said solid state switchingdevice for maintaining said solid state switching device in a conductingstate as said first capacitor charges to a predetermined voltage leveland for switching said solid state switching device to a nonconductingstate when said first capacitor charges to said predetermined voltagelevel, a second capacitor having a first terminal and a second terminalconnected across said first and second output electrodes of said solidstate switching device, and current responsive means coupled to saidsource of electrical energy and said second capacitor for charging saidsecond capacitor therethrough, said current responsive means switchingsaid solid state switching device to a conducting state when currenttherethrough declines to a predetermined level as said second capacitorcharges to a predetermined voltage level.